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All@ 7,1951 A. v. HAEFF ETAL MODULATOR 2 Sheets-Sheet l Filed Feb. 13,1946 mokmzmo mm-Oz cmi-.5mm

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- ANDREW 'V. HAEFF FRANKLIN H. HARRIS 7 1951 A. v. HAEFF ErAL MODULATOR2 Sheets-Sheet 2 Filed Feb. 13, 1946 Y if W V. HAEFF FRANKLIN H. HARRISPatented Aug. 7, 1951 MODULATOR Andrew V. laeil, Washington, D. C., andFranklin H. Harris, Accokeek, Md.

Application February 13, 1946, Serial No. 647,414

(Granted under the act of March. 3, 1883, as

.amended April 30, 1928; 370 0. G. 757) 14 Claims.

This invention relates to apparatus for generating high voltageelectrical impulses.

In many applications, including those related to radar operations and tocounter measures undertaken against radar operations, it is necessary togenerate high voltage electrical impulses which are timed accurately tocoincide with a control signal. In conventional circuit design,electrical impulses are generated by abruptly initiating or terminatingthe iiow of current in a resistor with a switch tube. Positive impulsesare obtained by terminating the ow of current in a plate resistor orinitiating a flow of current in a cathode resistor. If the plateresistor is used, the switch tube must be conducting between impulses;and if high voltage impulses from a low output impedance source arerequired, the powerv loss in the switch tube circuit will frequently bemore than can be tolerated. On the other hand, if the cathode resistoris used, no voltage ampliiication is possible unless the circuitsapplying the control or timing signal are operated about the potentialof the cathode terminal of the switch tube. The latter method, known at.bootstrapping, often involves design difficulties in that, ifadditional capacity is introduced between the cathode of the switch tubeand ground, the slope of the leading edge of the high voltage impulse isreduced.

This invention provides a method of generating high voltage impulses inwhich pulses off oscillations at a carrier frequency are generated,amplified, and rectified. The particular embodiment of the invention tobe disclosed is for use with an interference transmitter the pulsed out-Fig. 1 is a block diagram of a specific embodiment of the invention.

Fig. 2 is a schematic diagram of this embodiment of the invention. l

In accordance with Fig. 1, the control pulses of negative polarity areapplied at input terminal Il) to two pulse amplifiers, II and I6.

Carrier oscillator I2 is continuously operative at a high frequency;however, in the normal condition the iixed bias on the oscillator tubesis such that the output is very small. Amplified positive pulse signalsare applied from pulse amplifier II to the carrier oscillator, raisingthe bias of the oscillator tubes to effect oscillation at peakamplitude. The circumstance that carrier oscillator I2 is kept operativebetween pulses put of which is modulated with a signal comprising aspectrum of random frequencies commonly called a noise signal. Theinvention includes the means for modulating the high voltage impulses.

An object of this invention is to provide a means for generating highvoltage electrical impulses.

Another object of this invention is to generate pulses of the characterdescribed in the first object responsively to and coincident withcontrol signal pulses.

Another object of this invention is to provide a method of and a meansfor modulating impulses of the character described in the first objectwith a noise signal.

Other objects and features of this invention will become apparent from aconsideration of the following detailed description and the accompanyingdrawings in which:

makes possible a very rapid response to the control signals. If it werenecessary that oscillations be initiated with each pulse, the timerequired to build up oscillations to peak amplitude would be greaterthan could be tolerated.

The output of carrier oscillator I2 is coupled to carrier amplifier I3.The tubes of carrier amplifier I3 are normally biased below cut off, butare rendered conducting when carrier oscillator I2 is pulsed. The outputof the carrier amplifier I3 is inductively coupled to the rectifierstage I4 in which the pulses of carrier frequency oscillations aredemodulated for application to a transmitter. Plate detection is used,and the output I5 is taken from the cathodes of the rectifier tubes.Inductive coupling makes possible applying the signal from the carrierampliiier between the grids and cathodes of the rectiiier tubes with aminimum of complications.

In this embodiment of the invention, the output pulses are modulatedwith a noise signal. The noise signal is generated in noise generatorI8, amplified in the noise amplier and modulator Il from which it isapplied to the grids of the carrier amplifier tubes. Noise generator I8can be of any one of several devices known to the art for generating asignal which comprises the random interplay of a broad spectrum offrequencies. For best amplification of the noise signal, it is necessarythat the tubes of noise amplifier and modulator I1 be biased at a levelwhich is undesirable for continuous operation. Consequently the noiseamplifier and modulator I1 receives enabling bias in pulses from pulseamplier I6.

For a more detailed description of the circuits used in this embodimentof the invention, reference is made to Fig. 2.

Negative control pulses are applied from ter- 23 determines thefrequency of oscillation. Feedback is provided by a coil 23 connectingthe cathodes of the two tubes and inductively coupled to the coil oftuned circuit 21. 'I'he screen grids of tubes 25 and 25 are connected tothe plate of the pulse amplifier tube II, and, accordingly, in the nosignal condition are held at a voltage just sufiicient to allow thetubes to oscillate. However, when negative control pulses Iare appliedto the grid of pulse amplifier tube II, this tube is cut off, and itsplate voltage and that of the screen grids of tubes 25 and 26 rise to avoltage at which the carrier oscillator yields a maximum output. Theplates of tubes 25 and 25 are connected through a tuned circuitcomprising capacitors 30 and 3I and coil 32. The connection betweencapacitors 33 and 3l is grounded and the center tap of coil 32 isconnected to the positive side of a suitable power supply 3I and toground through capacitor 33.

The output of oscillator I2 is coupled to carrier amplifier I3 byinductive coupling between coils 32 and 34. Tight coupling is used tosimplify tuning.

Carrier amplifier I3 consists of tubes 35 and 35 connected in a pushpull amplifier circuit.

asomo? 4 monies from the output. It is apparent that the carrierfrequency must be substantially higher than any of the significantcomponents of the modulating signal.

Since the positive pulse output is taken from the cathodes of therectifier tubes, it is necessary that filament heater circuits and thebias generating circuits be operated with reference to the potential ofthese cathodes. Accordingly, a low v AIn the plate circuit of noiseamplifier 33 areresistors 3i and 33 and inductances 32 and 54-ar rangedin a manner known to the art to provide desirable peaking of the noisesignal. The plate of :pulse amplifier tube I6 is connected throughisolating resistor 33 to the plate circuit of noise amplifier tube 33 insuch away that the amplified signals from both tubes are mixed on thecommon plate inpedance comprising resistor 3| The input signal isapplied to the grids of these tubes from the terminals of coil 34.Capacitor 31, connected between thel grid of tube 33 and the plate oftube 35, and capacitor 33, connected between the grid of tube 35 and theplate of tube 35, serve as neutralizing condensers to prevent possibleself oscillation or regeneration. A negative bias is applied to thegrids of the tubes through the center tap of coil 34 from potentiometer43. 'Ihis bias is normally adjusted to reduce the carrier frequencyoutput of amplifier I3 to zero between pulses. The plates of tubes 35and 33 are connected by a tuned circuit consisting of capacitor 39 andcoil 40. The center tap of coil 40 is connected to the .positive side ofa suitable power supply 92 and to ground through capacitor 4I.

'I'he output of carrier amplifier I3 is coupled to the rectiiier I4 byinductive coupling between coils 43 and 42. Again tight coupling is usedto simplify tuning. Rectifier I4 consists of tubes '43 and 41 driven inpush pull as plate detectors,

the plates being grounded for radio frequencies through capacitors 53and 54, and the output being taken from the cathodes. 'I'he signal isapplied to both the screen and control grids of tubes 45 and 41 fromsuitable taps on coil 42.

The tubes are operated with a suitable bias obtained from dioderectifier and the filter network comprising resistor 43 and capacitors44 and 45. One terminal of the filter network is connected to thecathodes of the two tubes and and inductance 52. The mixed signal, whichconsists of noise modulated positive pulses, is applied to the controlgrids of the noise modulator tubes 11 and 13.

The noise modulator tubes 11 and 13 are operated in parallel for greaterpower output. A negative bias is applied to the control grids of thesetubes from the tap on potentiometer 15 through resistor 13. The positionof the tap on potentiometer 15 is adjusted so that these tubes will becut off in the no signal condition. The plate load impedance oi' the twotubes comprises resistors 19 and 3| and inductances 3II and 32 arrangedaccording to methods known to the art so as to eect peaking of the noisesignal. The output of the noise modulator tubes is applied throughcapacitor 33 to the center tap of coil 34 from which terminal litefi'ects grid modulation of carrier amplifier tubes 35 and 33.

It is apparent that, since the noise modulator tubes 11 and 13 receive apulsed enabling signal as well as the noise signal, the output of thesetubes comprises negative noise modulated pulses The negative pulsecomponent of this signal increases the negative bias on carrieramplifier tubes 35 and 35 during their operative periods and makespossible efficient class C amplification.

Although we have shown and described only a certain and specificembodiment of the invention, we are fully aware of the manymodifications possible thereof. Therefore, this invention is not to belimited except insofar as is necessitated by the spirit and the scope ofthe claims.

In the appended claims the word noise is intended to pertain to anelectrical signal comprising the random combination of a broad spectrumof frequencies.

The invention described herein may be manufactured and used by or forthe Government of the United States of .America for governmentalpurposes without the payment of any royalties thereon or therefor.

A What is claimed is:

1. A method of generating high voltage electrical impulses responsivelyto control signal pulses which comprises, developing oscillationscoincident with the start of each control signal pulse, maintainingoscillations during each control signal pulse, attenuating oscillationsat the end of each control signal pulse, and rectifying saidoscillations to form a high voltage impulse.

2. A method of generating high voltage electrical impulses responsivelyto and coincident with control signal pulses which comprises, generatingoscillations at a low amplitude level, in-

` creasing said oscillations to peak amplitude responsively to andcoincident with the start of each control signal pulse, maintaining saidoscillations at peak amplitude during each control signal pulse,restoring said oscillations to the low amplitude level at the end ofeach control signal pulse` and. rectifying the peak amplitudeoscillations only to form a high voltage impulse.

3. A method of generating high voltage electrical impulses responsivelyto control signal pulses which comprises, developing oscillationscoincident with the start of each control signal pulse, maintainingoscillations during each control signal pulse, attenuating oscillationsat the end of each control signal pulse, amplifying said oscillations,and rectifying said amplified oscillations to form a high voltageimpulse.

4. A method of generating high voltage electrical impulses responsivelyto and coincident with control signal pulses which comprises, generatingoscillations at a low amplitude level, increasing said oscillations topeak amplitude responsively to and coincident wth the start of eachcontrol signal pulse, maintaining said oscillatons at peak amplitudeduring each control signal pulse, restoring said oscillations to the lowamplitude level at the end of each control signal pulse, amplifying onlythe peak amplitude oscillations, and rectifying the amplifiedoscillations to form a high voltage impulse.

5. A method of generating high voltage modulated electrical impulsesresponsively to control signal pulses which comprises, developingoscillations coincident with the start of each control signal pulse,maintaining oscillations during each control signal pulse, attenuatingoscillations at the end of each control signal pulse, modulating saidoscillations, amplifying said modulated oscillations, and rectifyingsaid amplified oscillations to form a modulated high voltage impulse.

6. A method of generating high voltage positive electrical impulses,said impulses being coincident with control signal pulses and beingmodulated with a noise signal, which comprises the steps of generatinghigh frequency oscillations at a low amplitude lever between the controlsignal pulses, increasing these oscillations to peak amplituderesponsively to and during each control signal pulse, generating a noisesignal continuously, amplifying said noise signal only during thecontrol signal pulses, mixing said amplied noise signal and said peakamplitude oscillations to form a composite signal, amplifying saidcomposite signal, rectifying the amplied composite signal, and lteringthe rectied signal to form a noise modulated high voltage impulse.

7. Apparatus for generating high voltage electrical impulsesresponsively to control signal pulses which comprises, an oscillatorhaving a normally negligible output, means developing said outputoscillations responsive to each control signal pulse, means amplifyingthe oscillations from said oscillator, and means rectifying theamplified oscillations to form a high voltage impulse.

8. Apparatus for generating modulated high voltage electrical impulsesresponsively to control signal pulses which comprises, an oscillatorhaving a normally negligible output, means developing said outputoscillations responsive to each control signal pulse, means amplifyingthe oscillations from said osci1lator, means modulating said amplifiermeans. and means rectifying the amplied oscillations to form a modulatedhigh voltage impulse.

9. Apparatus for generating high voltage electrical impulsesresponsively to and coincident with control signal pulses whichcomprises, a high frequency oscillator generating low amplitudeoscillations between control signal pulses, means increasing theoscillations to peak amplitude during each control signal pulse, ampliermeans responsive to the peak amplitude oscillations only, and meansrectifying the amplified oscillations to form a high voltage impulse.

l0. Apparatus for generating high voltage electrical impulsesresponsively to and' .coincident with control signal pulses whichcomprises, a high frequncy oscillator maintained in continuousoperation; grid biasing means increasing the amplitude of the outputoscillations of said oscillator responsively to each control signalpulse; amplifier means receiving the output of the oscillator, saidamplifier means being responsive to the increased amplitude oscillationsonly, and means rectifying the amplified oscillations to form a highvoltage impulse.

11. Apparatus for generating positive high voltage electrical impulsesresponsively to control signal pulses which comprises; an oscillator;means normally biasing said oscillator for negligible output; saidbiasing means rendered inoperative responsive to each control signalpulse; means amplifying the oscillations from said oscillator; a cathodeloaded vacuum tube biased so as to be normally nonconducting;transformer means coupling said amplier means and said vacuum tube, theinput to said tube being applied between grid and cathode of said tube;and means filtering the output from the cathode of said tube to form ahigh voltage impulse.

12. Apparatus for generating positive high voltage electrical impulsesresponsively to and coincident with control signal pulses whichcomprises; an oscillator maintained in continuous operation; gridbiasing means increasing the amplitude of the output oscillations ofsaid oscillator responsively to each control signal pulse; ampliflermeans receiving the output of the oscillator, said amplier means beingresponsive to the increased amplitude oscillations only; a cathodeloaded vacuum tube biased so as to be normally nonconducting;transformer means coupling said amplier means and said vacuum tube, theinput to said tube being applied between grid and cathode oi said tube;and means filtering the output from the cathode of said tube to form ahigh voltage impulse.

13. Apparatus for generating positive noise modulated high voltageelectrical impulses responsively to and coincident with control signalpulses which comprises; an oscillator maintained in continuousoperation; grid biasing means increasing the amplitude of the outputoscillations of said oscillator responsively to each control signalpulse; a rst amplifier means receiving the output of the oscillator,said amplifier means being responsive to the increased amplitudeoscillations only; a source of noise signal; means amplifying said noisesignal, said noise amplifying means being rendered operative only duringsaid control signal pulses; means grid modulating said nrst amplifiermeans with the output from said second amplifier means; a cathode loadedvacuum tube biased so as to be normally nonconducting, transformer meanscoupling said first amplier means and said vacuum tube, the input tosaid tube being applied between grid and cathode of said tube; and meansfiltering the output from the .cathode of said tube to form a highvoltage noise modulated impulse.

14. Apparatus for generating positive noise modulated high voltageelectrical impulses responsively to and coincident with control signalpulses which comprises, an oscillator maintained in continuousoperation; grid biasing means increasing the amplitude of the outputoscillations of said oscillator responsively to each control signalpulse; a rst amplifier means receiving the output of the oscillator.said amplmer means being responsive to the increased amplitudeoecillations only; a source of noise signal; a source of pulsed enablingvoltage operative responsively to said control signal pulses; a secondampliner means receiving said noise signal and biased to be operative bysaid enabling voltage only during said control signal pulses, the outputof said second ampliner means comprising negative noise modulatedpulses; means grid modulating said mst amplifier means with the outputfrom said REFERENCES CITED The following references are of record in thele of this patent:

UNITED STATES PATENTS Number Name Date 1,872,398 Brown Aug. 16, 19322,113,214 Luck Apr. 5, 1938 2,398,097 Kent Apr. 9, 1946

